1. Field of the Invention
The present invention relates to a blue electroluminescent compound and an organic electroluminescent device using the same, and more particularly, to a blue electroluminescent compound containing a phenoxazine-based unit and an organic electroluminescent device having improved luminous efficiency and color purity by using the blue electroluminescent compound as a light-emitting component.
2. Description of the Related Art
Organic electroluminescent devices are active matrix emission type display devices in which, when an electrical current is applied to a fluorescent or phosphorescent organic compound layer (hereinafter, referred -to as an organic layer), electrons and holes are combined in the organic layer to emit light. Organic electroluminescent devices are light and comprise simple components and thus may be manufactured in a simplified process, and also have a wide view angle and display high quality images. Further, they can display high quality moving pictures with high color purity, and can be suitably used for portable electronic devices with low power consumption and low driving voltage.
Organic electroluminescent display devices can use either low or high molecular weight compounds, depending on characteristics of materials for forming organic layers and manufacture.
Many studies have been made about high molecular weight compounds since the discovery of the electroluminescence of poly(1,4-phenylenevinylene)(PPV), a π-conjugated polymer by Cambridge group in 1990. π-Conjugated polymers have an alternating chemical structure of single bonds (or σ bonds) and double bonds (or π bonds) , so that the polymers have delocalized π electrons capable of freely moving along with the polymer chain. The π-conjugated polymers have semi-conductive properties, and thus the whole visible light region corresponding to the HOMO-LUMO (highest occupied molecular orbital-lowest occupied molecular orbital) energy band-gap of polymers can be easily obtained through molecular design of the π-conjugated polymer, when the polymers are employed in an electroluminescent layer of an electroluminescent device. In addition, a thin film of polymer can simply be formed by spin coating or printing. Accordingly, the manufacturing process is very simple and cost-effective. Furthermore, the mechanical properties of a thin film of a π-conjugated polymer are excellent due to its high glass transition temperature. However, the device using high molecular weight compounds has several problems, including low color purity, high driving voltage, and low efficiency. Many studies have been made to overcome these problems. For example, U.S. Pat. No. 6,169,163 describes a method of copolymerizing fluorene-containing polymers to improve electroluminescent characteristics of organic electroluminescent devices. However, the improvement achieved is not satisfactory.
In manufacturing the device using low molecular weight compounds, an organic layer can be formed by vacuum deposition, the light-emitting materials can be easily purified to a high degree, and color pixels can be easily obtained. For practical application of the devices using low molecular weight compounds, however, there is still open for improvement in quantum efficiency and color purity, and a need to prevent crystallization of thin layers. Various studies on such electroluminescent displays using low molecular weight compounds have been actively undertaken, especially in Japan and the U.S.A. For example, Idemitsu-Kosan Co., Ltd. of Japan first exhibited in 1997 a 10-inch full color organic electroluminescent display using a color-changing medium. Pioneer Corporation of Japan presented a 5-inch passive matrix (PM) full color organic electroluminescent display. Recently, Pioneer Corporation and Motorola Inc. have arrived at an agreement concerning the mass production of cellular phones with an organic electroluminescent display, thus low molecular weight electroluminescent displays will be commercially viable in the near future.
Accordingly, there is an increasing need for a low molecular weight light-emitting compound which can simply form a thin film by vacuum deposition and spin coating or printing, similar to a high molecular weight compound, be used in dry and wet processes, and have an excellent blue light-emitting property.